After creating a new virtual directory from Visual Studio 2012 I found the Default Web Site was stopped. Trying to start it caused the following error:
"The World Wide Web Publishing Service (WWW Service) did not register the URL prefix http://*:80/MySite for site 1. The URL may be invalid. The site has been disabled. The data field contains the error number."
The only way I found to fix the problem was to edit the file C:\Windows\System32\inetsrv\config\applicationHost.config and remove/fix the faulty site declared in the sites section. In my case the URL of the site contained a slash that was in the oposite direction as compared to the other slashes in the URL.